Plasma drilling



Sept. 16, 1969 w. P. ACHESON ETAL 3,467,206

PLASMA DRILLING Filed July 7, 1967 2 SheetsSheet l AFMSQGV 56 4191770 34r 4/1 0 [QM/WIN ,rwarm/4.: i 600/?6235 IN VENTORS. W/LLARD P. ACf/ESOA/MICHAEL .4. 72786450 Sept. 16, 1969 w. P. ACHESON ETA!- 3,467,205

PLASMA DRILLING Filed July 7, 1967 2 Sheets-Sheet 2 Fig. 2

IN v ENTORS. M11490 RAG/550V M/fil/AEL 4. 7026450 United States Patent3,467,206 PLASMA DRILLING Willard P. Acheson, Pittsburgh, and Michael A.Torcaso, Arnold, Pa., assignors to Gulf Research & Development Company,Pittsburgh, Pa., a corporation of Delaware Filed July 7, 1967, Ser. No.651,830 Int. Cl. E21!) 7/18 US. Cl. 175-13 10 Claims ABSTRACT OF THEDISCLOSURE Method and apparatus for drilling wells in the earthutilizing a stream of disassociated gas (plasma) a reelable tubing toachieve wire line-like operation, and adding fiuxing agents to melt atthe bottom of the hole to automatically case the well as it is drilled.The plasma generator is mounted on the drill so that the stream ofplasma crosses the axis to cover the entire bottom of the hole as thedrill rotates.

This invention relates generally to the art of drilling wells in theearth, especially for the recovery of hydrocarbon deposits, and moreparticularly is directed to methods and apparatus for drilling suchwells utilizing plasma.

As used herein, the term plasma shall mean a stream of gas whosemolecules have been disassociated and ionized. A plasma generatortherefore is a device that produces such plasma. As is well known, whenplasma is directed at a target, the gas will reassociate, and willproduce tremendous quantities of heat at very high temperatures,temperatures on the order of 60,000 F. can be achieved. The presentinvention uses a plasma generator to drill wells.

The plasma drilling method of the present invention is not to beconfused with and is materially different from the so-called electricarc types of drilling. In said electric arc drilling means are providedto create an electric are at the bottom of the borehole, and the heat ofthe arc itself is utilized to crack and spall the formation. The heat istherefore very close to the electrodes and consumes them rapidly. Theelectric arc method also avoids melting of the formation because themelted rock would foul the equipment. In the present invention, the heatis transmitted by the plasma which releases its heat uponre-association, and the object is to melt the rock. The melted formationin the present invention will not foul the equipment because of theprovision of both the stream of plasma which itself keeps the meltedrock away from the plasma torch, and secondly, the stream of scourginggas which serves the same purpose, in addition to serving the purposesof cooling the plasma generator and as a carrier to bring the melted andaerated rock to the surface. Since the heat is released at points spacedfrom the generator, the electrodes are not so rapidly consumed.

Another feature of the present invention is that the drill head rotateswhile drilling the hole. Rotation of the drill head achieves advantagesover both electric arc and plasma type drills wherein the torch orgenerator is oscillated. In such oscillating head drills, the method isinherently discontinuous and therefore less eflicient. If the arc ofoscillation is less than 360 then an arcuate area will exist that willnot be positively drilled. If the arc of oscillation is more than 360then the overla region will be drilled twice which is a waste of timeand which causes lost motion of the drill head. Thus, by rotatinginstead of oscillating the drill head, the net effect is that the drillcuts faster and smoother without any dead spots, which results insmaller and more easily transported cuttings.

The method of the present invention is also materially different fromand has advantages over those types of drill bits wherein a flame isused to remove the formation. In the present invention, under normaloperating conditions, that is, in the absence of combustible fluids inthe formation, there will be no flame, In such prior flame drills, thereis a problem of keeping the flame away from the torch to prevent it fromdestroying the torch, there IS a problem both technologically andeconomically in supplying fuel to the torch, and there is a problem ofcorrosion since the products of combustion are corrosive to the drill.The present invention avoids all of these problems since there is nofuel supply, since the gas re-associates at zones spaced from thegenerator, and since there is no combustion and therefore no products ofcombustion.

One problem common to virtually all kinds of drilling methods presentlyin use is that a drill string, comprising long lengths of heavy walledpipe, is utilized to both transmit energy to the drill bit at the bottomof the hole, and to transmit cooling and chip carrier fluids, known asdrilling mud, to the bottom of the hole. Such drill strings are inthemselves expensive, require large amounts of energy to tum, andrequire considerable time to periodically remove from the hole forpurposes of changing the bit, and for other purposes.

Another problem present in conventional types of drilling is that thesides of the borehole are left unprotected as depth increases. This isoften a problem when unconsolidated formations, such as loose sand orthe like, are encountered. The problem is solved, conventionally, bycasing the well, which comprises removing the drill string from thewell, inserting relatively large diameter pipe into the well to the zoneit is desired to case off, and then filling the space between theoutside of the pipe and the side of the borehole with cement, to therebyseal off the troublesome zone. Casing is an expensive and time consumingprocedure. The present invention eliminates or at least substantiallyreduces the amount of casing that must be done by means of the inclusionof fluxing agents into the scourging or ionizing gas. When such fluX-ing agents are exposed to the very high temperature which will begenerated at the bottom of the borehole during drilling, they will melt,and in effect, a lining for the side of the borehole will be created asa by-product of the drilling operation and simultaneously therewith. Theparticular flux used will depend upon the nature of the formation beingdrilled.

In the accompanying drawing forming a part of this disclosure: FIG. 1 isa diagrammatic vertical cross-sectional view of the apparatus of theinvention showing the plasma drill of the invention drilling a well; andFIG. 2 is a longitudinal cross-sectional view through the drill of theinvention.

Referring to FIG. 1, there is shown a borehole 10 which is being drilledby plasma drill 12. The surface equipment includes a well head 14. Itwill be understood that well head 14 is diagrammatic only, and willinclude but does not show conventional safety equipment such as blow-outpreventers, and other conventional equipment well known to those skilledin this art. Drill 12 is connected to the surface by a composite cable16 which connects the drill to a reel 18 mounted on a reel support 20.Preferably, reel and reel support 18 and 20 are mounted close to and maybe a part of a derrick assembly 22 which includes guide rollers 24 whichguide cable 16 and drill 12 in vertical motion in the well 10.

As will appear more clearly in the detailed description of drill 12below, the drilling method of the invention requires that ionizing gas,scourging air, electricity for the electrodes within the plasmagenerator, and electricity to turn the plasma generator be suppliedthrough cable 16 from the surface to the drill 12. In some cases, itwill also be desirable to supply fluxing agents through the cable to thedrill.

Reference numeral 26 designates a black box labeled Energy and MaterialsSources in FIG. 1. This black box indicates the various pieces ofequipment that supply the above energies and materials to cable 16 fordelivery to drill 12. It will be understood that any suitable means maybe used for the supply functions. For example, the ionizing gas may besupplied by a pump. The two separate electrical currents may be suppliedby generators on the drill site, or by connection to utility companyservice lines in the area if such are available. The scourging air maybe supplied by tank trucks of compressed air, on-site compressors, orthe like, and means such as a gravity feed hopper, aspirator, screwfeeder, or the like, may be used to supply the fluxing agents inpowdered form. Supply conduits, generally indicated by conduit 28,connect the energy and material sources to the hub 30 of reel 18, andvarious electrical brush and rotating valve assemblies, not shown, areprovided within hub 30 to transmit the energy and materials to thevarious parts of cable 16, as will be described more clearly below.

Reference numeral 32 designates a black box labeled Separation Equipmentin FIG. 1. This black box indicates equipment to separate the formationmaterial removed by drill 12, equipment to detect any fluids such ashydrocarbon liquids or gases that may be included in such material, andequipment to vent the cleansed air after the above matter is removedfrom it. It will also include equipment to flare gas if gas is used asthe scourging fluid. Separation equipment 32 serves the function of themud tanks, pumps, shale shakers, and the like used in conventionalrotary drilling. The formation removed by the drill 12 will be returnedto the surface in the form of a crystallized froth or as solidifiedaerated globules, and these cuttings may be removed from the air byappropriate equipment such as screens, cyclones, settling chambers, orthe like. A conduit 34 connects the separation equipment 32 to well head14 and communicates the annulus between the borehole 10 and the cable 16with the separation equipment. As in conventional drilling, the energyand materials are supplied through the cable, analogous to the drillstring, and returned via the annulus.

Referring to FIG. 2, drill 12 is essentially a two-part structurecomprising an upper member 36 and a lower member 38. Upper member 36serves as a weight and stabilizing bar, and as an energy and materialdistribution point for the drill.

Upper member 36 comprises a main body member 40 formed with suitableconnection means, such as a threaded nipple 42, to receive the lower endof the outside wall 44 of cable 16. A collar member 46 is threaded onnipple 42 and holds the lower end of the outside wall 44 of cable 16onto the drill 12. The connection means 42, 46 is exemplary only, and itwill be understood that various means are available to attach the cablewall to the upper end of the drill. The outside wall of cable 16 may beformed of any suitable material which will bear the weight of the drill,and which will allow itself to be reeled. Within outside wall 44 cable16 includes a relatively small diameter conduit 48 which carries theionizing gas, and a second small diameter conduit 50 which carries theelectrical leads. The ID. of outside wall 44 is considerably larger thanthe sum of the diameters of conduits 48 and 50, and the relatively largeannulus inside wall 44 is used to transmit the scourging fluid,preferably air, to the drill head, as will be explained below. Ifdesired, the conduits 48 and 50 could be fabricated integrally withoutside wall 44. Gas carrying conduit 48 could be a flexible metaltubing, and electrical lead carrying conduit 50 could be of insulated,multi-wire construction.

Since plasma generators are essentially high amperage/ low voltagedevices, and since the required electrical lead diameter is a functionof amperage, it may be desirable to include a downhole transformer inupper member 36, along with associated rectifying equipment to convertthe energy to DC. This equipment is not shown in the drawing, but it maybe easily provided in upper member 36, if it should be desired. It isdesirable to work with relatively thin electrical leads as far aspossible, from the economy viewpoint, and from the viewpoint of keepingthe total size of the reelable cable 16 as small as possible.

Main body member 40 serves as a weighting member to maintain the drillstable in the hole and to aid it in its downward movement as it drillsthe hole. The upper member 36 is shown broken to indicate that anylength of member 40 could be provided dependent upon the amount ofweight desired, and, as will be explained below, the upper member 36 canbe readily changed during the drilling of a hole. Additional means areprovided to stabilize the drill in the hole. To this end, a pair ofspring loaded arms 52 are hinged to the top of the body member as at 54and are biased outwardly against the sides of the borehole 10 by springs56. As will be understood by those skilled in this art, more than twoarms 52 could be provided. The arms 52 serve to centralize the drill inthe hole, and other types of centralizers such as how springs could beprovided in their place.

Upper member 36 is provided with a longitudinal central opening 58through which the conduits 48 and 50 pass, and which is in communicationwith the inside of cable 16. Thus, longitudinal opening 58 serves as ascourging gas conduit to deliver the scourging gas to the drill.

Means are provided to permit quick connection and disconnection of gasand electrical conduits 48 and 50 between upper member 36 and lowerdrill member 38. To this end, a cover plate 60 is provided at the lowerend and at one side of upper member 38. Suitable means such as gasket 62and bolts 64 are provided to permit ready removal of the cover plate.Under cover plate 60, body member 40 is formed with a radial opening 66in which is mounted a terminal block 68 in which are removably mounted aquick disconnect coupling 70 for the electrical conduit 50 and a quickdisconnect coupling 72 for the gas conduit 48. Lower member or drill 38includes a protective sheath 74 which extends into a suitably formedopening in cover plate 60 and through which passes electrical leads 76and gas lead 78 which lead to the quick disconnect couplings 70 and 72,respectively. At its extreme lower end, body member 40 is formed with aconventional drill pipe box or female pipe thread connection 80, whichcooperates with a pin or male connection 82 on the upper end of drill38. Suitable conventional sealing means, not shown, may be providedbetween pin and box connection 80, 82.

Thus, the upper weighting and stabilizing member 36 can be asembled ordissembled from the drill, or a heavier or lighter member can beprovided, by removing cover plate 60, breaking quick disconnectcouplings 70 and 72, and breaking thread connections 80, 82.

Drill 38 comprises an axial longitudinal chamber 84, which is in tandemwith opening 58 to provide a continuous passageway from the inside ofcable 16 to the drill head through the drill and the upper member. Afterits passage through sheath 74 gas lead 78 passes through a suitableradial opening 86 in the body of drill 38 to a rotary seal device 90positioned in air chamber 84. Rotary seal 90 is held in place by anysuitable means such as struts 92. A rotating gas delivery pipe 94 isconnected to the lower end of rotary seal 90 and delivers the ionizinggas to the plasma generator 96 located in the rotary drill head 98, aswill be described below.

Means are provided to rotatably mount and to cause rotation of rotarydrill head 98 with respect to drill body 88. To this end drill body 88is of a generally elongated U-shaped configuration in cross section toreceive a stem portion 100 of rotating drill head 98. Upper bearing 102and lower bearing 104, of conventional anti-frictional roller or othertype, is provided between the drill body 88 and drill head stem 100.Drill 38 includes a motor 106 which drives the drill head. The stator108 of motor 106 is mounted by means of suitable electrical insulation110 in drill body 88, and the rotor 112 with suitable insulation 114 ismounted in stem portion 100 in juxtaposition to the stator. Electricalenergy is supplied to stator 108 by a pair of the electrical leads 76after they pass through sheath 74. Four sets of electrical brushes andcommutator assemblies 116 are provided between body 88 and stem portion100. Two brush assemblies 116 are used to transmit electrical energydelivered by two of the leads 76 to rotor 112 of motor 106, Theremaining two brush assemblies 116 pass through a conduit 118 inrotating head 98 and deliver electrical energy to the plasma generator96.

As shown, motor 106 comprises only one rotor/stator stage. It will beunderstood that more than one such stage, with the appropriate brushassemblies 1'16, may be provided to provide a more powerful motor. Thedrill is shown broken between lower bearing 104 and motor 106 toindicate the inclusion of additional electrical motor stages, ifrequired.

As explained above, the scourging gas passing through cable 16 andpassageways 58 and 84 to the bottom of the borehole serves severalimportant functions, i.e., cooling of the plasma generator 96, as avehicle to carry the melted formation particles away, and to aid indirecting the stream of plasma away from the generator. Therefore, thelower end of rotating drill head 98 is formed with several differentpassageways each of which receives some of the scourging gas and whichserve these various purposes. Passageways 120 and 122 are directedupwardly from the generator and stream of plasma and serve primarily topush the cuttings up the annulus to the surface. Passageway 124 isdirected downwardly and tangentially at a small angle to the directionof the plasma stream and serves primarily to direct the plasma streamaway from the generator. Passageway 126 is connected to the internalcooling passageways within the generator, and serves primarily to coolthe generator. A passageway 128 exhausts the air supplied throughpassageway 126 and also serves to direct formation particles out towardsthe sides of the borehole. It will be understood that the passageways122 through 128, shown and described, are but representative of thevarious types of passageways and that several of each type of passagewaymay be provided.

The lower end of rotating head 98 is of triangular crosssection andincludes the lowest part of the drill. At said lowest part an idlerroller assembly 130 is provided which guides the rotational motion ofthe drill head. Roller assembly 130 comprises an axle 132 and an idlerroller 133 which comprises a hemispherical end face 134, joined to thebody of the roller by a sharp edge 136. Thus, the roller makes a slidingpoint contact with the side of the borehole on hemispherical portion134, and a rolling contact with the bottom of the borehole on edge 136.

The plasma generator 96 is disposed at an angle and is directeddownwardly with respect to the axis of the drill, and is positioned toone side of said axis with its exit orifice close to said axis, so thatthe stream of plasma will cross the axis and travel a distance greaterthan the transverse radious of the hole. The length of said stream isadjustable by adjusting certain parameters within the generator, such asthrottling means for the ionizing gas and the physical configuration ofexit orifices and the like, and is set so that the effective length ofthe stream will be such that a hole having the desired diameter will beproduced. The bottom of the hole will therefore have a cone or hill-likeconfiguration as shown.

By locating the plasma generator as described, the generator will drillacross the axis of the hole, which results in accurate control of holediameter. The generator may be adjusted and controlled, from thesurface, by increases or decreases in one or both of the supply ofionizing gas or electrical power.

By so directing the plasma stream in combination with the inclusion offluxing agents, which will melt and migrate towards the side of theborehole, the advantage of obtaining a self-casing borehole will beobtained, The finely powdered particles of fiuxing agent in either theionizing gas or scouring gas will melt, and when directed outwardly bythe stream of plasma, as primarily by the passageways 124 and 126, willcoat the side of the borehole with a glass-like lining. The fluxingagents will be so finely powdered that they will not clog any of thepassageways in the generator or the rotating drill head. Suitablematerials for use as the fiuxing agent include borax, feldspar, siliconoxides, or other suitable minerals, dependent upon the nature of theformation being drilled. The ionizing gas is preferably a diatomic inertgas such as argon, nitrogen, or suitable other gases or combinations ofgases. The scourging gas is usually air, but in those cases where it isanticipated the hydrocarbon deposits will be in the form of natural gas,air is not desirable because of the explosion danger. In such wells,gas, methane or natural gas readily available in many oil fields, may beused as the scouring gas, or even the exhaust gases from the variousengines on the drill site, properly treated to remove solids andcorrosive agents, could be used as the scouring gas.

The intense heat generated by the re-association of the gas will meltthe rock. The relatively large amount of scourging gas, air or methaneor whatever is being used, added into the molten rock will cause therock to froth trapping bubbles of this gas as well as bubbles of there-associated gas as the rock cools, resulting in a light material whichmay be easily driven up the annulus. The molten froth will, because ofits light weight and rapid motion, quickly give up its heat primarily tothe surrounding formation, and will then be carried up to the surfaceand delivered to separation equipment 32. The scourging gas will alsohelp to cool the cuttings.

We claim:

1. A method of drilling earth boreholes with plasma comprising the stepsof rotatably mounting a plasma generator on a drill, holding the body ofthe drill stationary with respect to rotation about the axis of thedrill, rotating the plasma generator about the axis of the drill,directing the stream of plasma produced by the plasma generator from oneside of the axis of the drill at an angle to said axis acros said axisand over the entire bottom of the borehole during each revolution of thegenerator, and lowering the drill as the drill creates the borehole.

2. A method of drilling earth boreholes with plasma comprising the stepsof rotatably mounting a plasma generator on an axially rotatable drillto direct the stream of plasma produced by the plasma generator from oneside of the axis of the drill at an angle to said axis across said axisand over the entire bottom of the borehole during each revolution of thegenerator, mounting said drill on a reelable cable, supplying electricalenergy to said plasma generator through said cable, supplying electricalenergy to a motor in said drill through said cable to cause said plasmagenerator to rotate with respect to said drill, supplying adisassociatable gas to said plasma generator, supplying a stream ofscourging gas to said drill through said cable, and lowering said drillon said reelable cable as said drill creates the borehole.

3. The method of claim 2, and supplying finely powdered fluxing materialto said scourging gas.

4. The method of claim 2, and supplying finely powdered fiuxing materialto said disassociatable gas.

5. Apparatus for drilling earth boreholes comprising a drill, a plasmagenerator mounted on said drill, means to cause rotation of saidgenerator about the axis of said drill, cable means connected to theupper end of said drill, means to reel and unreel said cable means fromthe surface to raise or lower said drill in the borehole, and saidplasma generator being mounted on one side of said drill with respect tothe axis thereof and disposed at an angle with respect to the axisthereof and with the plasma outlet end of said generator close to theaxis thereof, whereby the stream of plasma issuing from said generatorwill flow across the axis of said drill.

6. The apparatus of claim 5, said means causing rotation of saidgenerator about the axis of said drill comprising an electrical motor,said motor comprising a motor stator mounted on a body portion of saiddrill, means to hold said body portion stationary with respect torotation about the axis of said drill, said drill comprising a stemportion rotatably mounted within said body portion of said drill, saiddrill comprising a drill head portion forming part of said drill stemportion, said motor comprising a motor rotor mounted on said drill stemportion in juxtaposition to said motor stator, said plasma generatorbeing mounted on said drill head portion, and means to supply electricalenergy to said motor rotor and said motor stator from the surfacethrough said cable means.

7. The apparatus of claim 5, said drill comprising a body portion, meansto hold said drill body portion stationary with respect to rotationabout the axis of said drill, said drill comprising a rotating portioncarrying said plasma generator, and motor means disposed on saidstationary portion and said rotating portion to power said rotatingportion with respect to said stationary portion.

8. The apparatus of claim 5, said drill comprising an upper member and alower member, means to removably join said upper member to said lowermember, said upper member and said lower member being formed with axialpassageways in communication with each other and in communication withthe central opening within said cable means, whereby a flow of scourginggas may be supplied from the surface through said cable means and thepassageways in the portions of said drill to said generator and thebottom of the borehole; said upper member comprising a weighting andstabilizing member, and said lower member comprising a drilling member.

9. The apparatus of claim 5, and cable means including means to supply aflow of disasociatable gas from the surface to said plasma generator,said cable means including means to supply electrical energy from thesurface to said plasma generator, and said cable means including meansto supply a flow of scourging gas from the surface to the vicinity ofand to said plasma generator.

10. The apparatus of claim 9, said drill comprising an upper weightingand stabilizing member and a lower drilling member, said upper and lowermembers being formed with communicating axial passageways which alsocommunicate the space within said cable means with the bottom of saidborehole and said plasma generator, said upper member comprising quickdisconnect means adapted to quickly connect and disconnect saidelectrical energy supply means and said disassociatable gas supplymeans, said scourging gas supply :means comprising said communicatingpassageways within said upper and lower members, and means to connect ordisconnect said upper and lower members, whereby said upper and lowermembers may be readily separated from each other for replacement ofeither of said upper and lower members.

References Cited UNITED STATES PATENTS 2,327,496 8/1943 Burch -132,816,735 12/1957 Dalinoa et a1. 175-15 3,045,766 7/1962 Fleming 175-14ERNEST R. PURSER, Primary Examiner US. Cl. X.R. 175l4, l5

